It is generally known that motor vehicles, such as automobiles, are provided with aids to enable observation of what is happening on the side of and behind the automobile. Often, such aids are designed as wing mirrors. Normally, a wing mirror comprises a cupshaped housing which is fitted on a more forward part of the side of the motor vehicle and in which a mirror element is accommodated. The mirror element is often substantially plate-shaped and includes an angle with the main axis of the motor vehicle both in the horizontal plane and in the vertical plane. The horizontal and the vertical angles depend inter alia on the length and the personal preferences of the driver of the motor vehicle. To enable the desired angles for each driver to be set, the mirror element is connected with the mirror housing so as to be pivotable about at least one pivoting axis, but often about two pivoting axes mutually including a right angle.
Because the angles desired by a driver can normally be assessed only from the driver's seat of the vehicle, and because the driver normally cannot adjust the mirror element manually from this position, it is desirable that the position of the mirror element in the wing mirror can be adjusted remotely by means of an actuator mechanism.
Preferably, the actuator mechanism then comprises an electric motor and a mirror adjusting element movably coupled therewith via a drive train. Owing to the use of an electric motor, the actuator mechanism can be made of relatively compact design, while with the aid of the drive train, a relatively fast rotation of the output shaft of the electric motor can be converted into a relatively slow movement of the adjusting element, so that the angular position of the mirror element in the wing mirror can be accurately set.
To realize, with the aid of the drive train, an appropriate reducing transmission between the electric motor and the mirror adjusting element, it has previously been proposed to implement the drive train as a gear train, the gears of which are provided with a conventional involute toothing.
Although an actuator mechanism provided with such a gear train can be manufactured at a relatively low cost price, such a conventional involute gear train has the disadvantage that a continuous mesh between two cooperating gears can only be realized when each gear carries at least six teeth along the circumference. In view of the limited construction space available for the actuator mechanism in the mirror housing, the gear train must consequently be implemented in practice with several transmission steps to realize the relatively large reduction of the rotational speed of the output shaft of the electric motor that is required for this application. This has as a disadvantage not only that the manufacturing costs of the drive train increase, but also that the efficiency of the transmission decreases, so that a heavier and more expensive electric motor must be chosen. In addition, the use of several transmission steps in the gear train leads to a greater play in the drive, which, during use, may lead to an undesirable vibration of the mirror element coupled with the mirror adjusting element.
Because of the above-mentioned problems, mirror actuator mechanisms are designed with a drive train which comprises a worm mounted on the output shaft of the electric motor, which worm drives a worm wheel. Such a mirror actuator mechanism is described in the German patent application DE 199 12 685. In this actuator mechanism, the worm wheel is provided with an inner thread which is in engagement with a spindle provided with an outer thread, which spindle forms the mirror adjusting element. During use, the worm mounted on the output shaft of the electric motor causes the worm wheel to rotate, while the inner thread of the worm wheel in engagement with the outer thread of the spindle functions as a rotation-translation converter, so that the spindle can move back and forth along the axis of the worm wheel. To enable manual adjustment of the mirror element in case of failure of the electric motor, the inner thread is connected with the worm wheel in a radially resilient manner, so that through elastic deformation the connection between inner thread and outer thread can be temporarily broken. As a result, the mirror adjusting element can be displaced in axial direction by jerks when the mirror element is pivoted manually relative to the mirror housing.
A disadvantage of the known actuator mechanism equipped with a worm wheel transmission is that it is relatively complex to manufacture and that it has a still lower efficiency, so that a relatively large and expensive electric motor must be chosen after all.